Associated Forest Cover
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Throughout its range, honeylocust generally occurs only as a minor
component of natural forest stands. It is included in four forest
cover types in the United States (19). It is an associated
species on lowland sites in Bur Oak (Society of American
Foresters Type 42), especially in the more southerly portions of
the type range, and in Willow Oak-Water Oak-Diamondleaf Oak (Type
88). It is a minor associate in Sweetgum-Willow Oak (Type 92) and
Sugarberry-American Elm-Green Ash (Type 93). Mesophytic species
commonly associated with honeylocust include red maple (Acer
rubrum), persimmon (Diospyros virginiana), blackgum
(Nyssa sylvatica), pecan (Carya illinoensis), boxelder
(Acer negundo), Kentucky coffeetree (Gymnocladus
dioicus), black walnut (Juglans nigra), oaks (Quercus
spp.), elms (Ulmus spp.), ashes (Fraxinus spp.),
and hickories (Carya spp.).
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Climate
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In the western portion of its range honeylocust grows in a
subhumid climate while in the middle and eastern portions the
climate is humid. Normal annual precipitation varies from about
510 mm (20 in) in South Dakota and Texas to more than 1520 mm (60
in) in southern Louisiana, Mississippi, and Alabama. Average
annual snowfall varies from none to 102 cm (40 in). Length of the
growing season varies from about 150 days in the north and
northeast to more than 300 days in the southern extremities of
the range.
Honeylocust is tolerant of low temperatures and in the north it is
hardy at -29° to -34° C (-20° to -30° F)
(10). Northern races harden-off and become dormant relatively
early, while growth of southern races continues later into the
year. Southern races are subject to frost damage when planted in
the north (7). Honeylocust also may suffer frost damage or
dieback because of its indefinite or indeterminate annual growth
pattern (4). Twigs may continue to elongate until stopped by
cold, whereupon the tender terminal internodes are killed by the
first frosts. New growth in the spring then comes from the lower
lateral buds.
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Damaging Agents
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With the increased popularity and
plantings of honeylocust, particularly the cultivars of thornless
varieties, there has been a corresponding increase in the kinds
and numbers of attacking insects. Generally, insect attacks are
not fatal but they do weaken the tree and retard growth.
Honeylocust is a host of a number of leaf feeders and severe
infestations can rapidly defoliate trees. A severe and widely
distributed defoliator is the mimosa webworm (Homadaula
anisocentra) (1). The search for webworm resistant trees has
not been productive (17). Eotetranychus multidigituli, a
spider mite common to the midwest, and other mites feed on
honeylocust leaves. Heavy infestations, occurring particularly in
hot dry weather, will defoliate a tree. The whitemarked tussock
moth (Orgyia leucostigma), the honeylocust plant bug (Diaphnocoris
chlorionis) (25), the leaf hopper (Empoasca pergandei),
and several other species of pod galls, leaf rollers, leaf
hoppers, moths, loopers, bagworms, and beetles feed on
honeylocust foliage. The walkingstick (Diapheromera femorata)
is also included among the many defoliators (21).
Agrilus difficilis, a flatheaded borer, important west of
the Mississippi River, burrows beneath the bark and may
eventually girdle the trunk or large limbs (18). Several other
bark and wood borers attack honeylocust, such as the widely
distributed Xyleborus saxeseni.
A number of scale insects, such as the European fruit lecanium
(Parthenolecanium corni), which is widespread and
particularly damaging to shade trees, and the cottony maple scale
(Pulvinaria innumerabilis), injure the bark of
honeylocust, especially on small branches, lowering the vitality
and growth rate of trees (18). Weakened trees become subject to
attack and further damage by various species of boring insects
and bark beetles.
The twig girdler, Oncideres cingulata, prunes small
branches and can inflict severe injury on nursery seedlings.
Heavy infestations can also severely damage large trees. The
larvae of Amblycerus robiniae, a bruchid weevil, feed on
honeylocust seed (1). The female periodical cicada (Magicicada
septendecim) can damage honeylocust, especially young
transplanted trees, by depositing eggs in the twigs.
Honeylocust is subject to few diseases, none of which interfere
with its growth, except in isolated situations. The most
noteworthy disease is the canker Thyronectria
austro-americana, which can be fatal. Spiculosa cankers cause
loss in merchantable wood volume or cull. Honeylocust is subject
to several heart-rot and wood-decay fungi from species of Fomes
and Polyporus.
Few leaf diseases attack honeylocust, and none mar the tree. The
most widely distributed is tarry leaf spot caused by Linospora
gleditsiae (9). In the seedling stage honeylocust is
susceptible to cotton root rot (Phymatotrichum omnivorum),
which is sometimes fatal (7). In shelterbelt planting tests
in Oklahoma and Texas it was ranked as highly susceptible to
certain Phymatotrichum root rots (27). Two other root
diseases, Ganoderma lucidum and G. curtisii, can
cause extensive root rot and tree fatality. The incidence of
these root rots is not high.
In the southeast Texas area honeylocust was visibly damaged but
not killed by air pollution, presumed to be mainly sulfur
dioxide. In Illinois the species was ranked as highly resistant
to ice damage and in Tennessee it was rated about average in
resistance to flooding damage (9). It also appears to be
resistant to salt spray when planted near the coast. Honeylocust
is considered to be windfirm, but heavy limb breakage from wind
was reported in Kansas. Because of its relatively thin bark it is
easily damaged by fire (7). Rabbits sometimes inflict damage by
gnawing the bark from young trees during the winter.
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Flowering and Fruiting
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Flowering occurs in late spring,
the average date being about May 10 in the southern limit of the
range and June 25 in the north (7). Honeylocust leaves are nearly
full grown when the flowers are produced, which is usually late
enough in the year for the seed crop to escape frost damage.
The species is polygamo-dioecious; flowers are home in axillary,
dense, green racemes (24). Racemes of staminate flowers are 5 to
13 em (2 to 5 in) long, pubescent, and often clustered. The calyx
is campanulate, with five elliptic-lanceolate lobes; there are
four to five petals, erect, oval, and longer than the calyx
lobes; and up to 10 stamens, inserted on the calyx tube. The
pistil is rudimentary or absent in the staminate flowers.
Pistillate racemes are 5 to 8 ern (2 to 3 in) long, slender, with
few flowers, and usually solitary. The pistils are tomentose, the
ovary nearly sessile, and the style short; there may be two
ovules or many. The stamens are much smaller and abortive in
pistillate flowers.
Seeds, borne in long (15 to 41 cm, 6 to 16in), flat, indehiscent,
and often twisted pods, ripen about mid-September in the southern
portion of the range and around mid-October in the north. Soon
after fruits mature they begin falling and dissemination often
continues into late winter.
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Genetics
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Races and Hybrids
The honeylocust has wide genetic variations that have enabled
improvement through selection. The northern races show relatively
good winter hardiness and southern races bear fruit that is much
more nutritious for stock feeding than that found on the trees in
the north (6).
A number of horticultural forms have been developed and are widely
cultivated, especially for shade and as ornamentals (24).
Thornless honeylocust (Gleditsia triacanthos var. inermis
Willd.) is thornless, or nearly so, and slender in habit;
bushy honeylocust (G. triacanthos var. elegantissima
[Grosdemangel Rehd.) is unarmed and densely bushy; Bujot
honeylocust (G. triacanthos var. bujotii [Neuml
Rehd.) has slender pendulous branches and narrow leaflets; and
dwarf honeylocust (G. triacanthos var. nana [Loud.]
A. Henry) is a small compact shrub or tree. Selected cultivars of
the thornless forms have been patented. About 60 percent of the
seedlings grown from thornless honeylocust seed are thornless
(7).
Gleditsia x texana Sarg., the Texas honeylocust, is
considered to be a hybrid of G. aquatica Marsh. and G.
triacanthos L. (24). Its range is largely restricted to the
Brazos River bottoms in Texas, with additional trees found along
the Red River in Louisiana and occasionally along the Mississippi
River in Indiana and Mississippi.
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Growth and Yield
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In natural stands honeylocust attains a
height of 21 to 24 m (70 to 80 ft) and a d.b.h. of 61 to 91 cm.
(24 to 36 in). On the best sites, trees may be 43 m (140 ft) in
height and 152 to 183 cm (60 to 72 in) in d.b.h. On poor sites
trees are stunted, wide-branched, and often covered with thorns.
In eastern Nebraska, 18- to 35year-old honeylocust in plantations
grew an average of 4.6 cm (1.8 in) in diameter each 10 years.
The average height growth of honeylocust planted in shelterbelts
from North Dakota to Texas was 49 cm (19.2 in) per year during
the first 7 years (7). This was a slower height growth than for
plains cottonwood (Populus deltoides var. occidentalis)
and Siberian elm (Ulmus pumila) but faster than that
of American elm (U. americana), green ash (Fraxinus
pennsylvanica), or hackberry (Celtis laevigata), all
of which were frequently planted on the same shelterbelt
projects. Under favorable conditions the annual diameter growth
of young honeylocust is from 8 to 13 mm (0.33 to 0.50 in) (22).
The species is an excellent tree for windbreaks.
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Reaction to Competition
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Honeylocust is classed as
intolerant of shade, and reproduction becomes established only
beneath openings in the forest canopy (5). Both top and root
growth are retarded where young trees are subjected to shade;
therefore, for survival and optimum development, honeylocust must
maintain a dominant position in the forest community. Lower limbs
of forest-grown trees die when they are excessively shaded from
the
sides, and the dead limbs often are retained for some time.
Honeylocust is occasionally a pioneer on midwest strip-mine spoil
banks. It is also a pioneer in rocky limestone glades of
Tennessee and Kentucky, where it is often succeeded by eastern
redcedar (Juniperus uirginiana). In northern Ohio,
honeylocust was found with shellbark hickory (Carya
laciniosa) and bur oak (Quercus macrocarpa) in the
elm-ash-soft maple association on areas that formerly were swampy
(7).
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Rooting Habit
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Honeylocust is deep rooted with a widely
spreading and profusely branched root system and a strong
taproot. Deep soils are penetrated as far as 3 to 6 m (10 to 20
ft). The root system is responsive to environmental conditions.
For example, in a Missouri study, 4- to 6-year-old saplings on
upland clay soil produced root systems that were about twice as
long, with laterals covering twice the area, as those of older
trees growing in lowland alluvial soil where the water table was
higher (7). The generalized, well-developed root system enables
this species to grow on both upland and lowland sites.
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Seed Production and Dissemination
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Honeylocust begins
bearing seed at about 10 years of age, optimum production
occurring between 25 and 75 years. Trees continue to bear fruit
up to about 100 years of age (7). They generally bear fruit each
year and produce abundant seed crops every year or two.
Honeylocust seeds, like those of many leguminous species, have
impermeable coats and thus remain viable for long periods of
time. Under natural conditions, individual seeds become permeable
at different periods following maturation so that any one crop is
capable of producing seedlings over a period of several years.
The seeding range or natural dispersal of honeylocust seeds is not
extensive. The pods, however, are readily eaten by cattle,
whereby seeds are scattered in the feces. Undoubtedly seeds are
also disseminated by birds and other mammals that feed on the
fruit. Cleaned seeds average about 6,170/kg (2,800/lb), with a
commercial purity of 95 percent and a soundness of 98 percent
(24). Viability can be retained for several years when seeds are
stored in sealed containers at 0° to 7° C (32° to
45° F) (3).
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Seedling Development
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Germination is thought to be
enhanced when seeds are eaten and passed undigested by birds and
mammals (7). Passage through the digestive system apparently
softens the impermeable seedcoat. Enhanced germination can also
be achieved by mechanically scarifying the seeds or soaking them
in concentrated sulfuric acid or hot water (880 C, 1900 F) for 1
to 2 hours. When hot water is used the water and seeds should be
allowed to cool to room temperature or until seeds swell (3).
Treated seeds should be sown promptly and not stored. Germination
is epigeal.
Honeylocust seedlings show a growth pattern characteristic of
deciduous hardwoods with sympodial. growth. Persistent terminal
buds are not formed and the shoot tip often dies and falls off
(5).
Nursery-grown seedlings from pretreated seeds attain suitable
size-30 cm (12 in) or more in height-for field planting in 1 year
(3). In southern Michigan, first-year seedlings grown in pots
reached a height of 37 cm (14.6 in) by September 21, just before
leaf abscission (5). The average root-to-shoot ratio was 2 to 3.
Stem growth was slow in the spring but rapid in early summer and
fall. Only 60 percent of the height growth was attained by
mid-July. In an additional study in southern Michigan, nursery
seedlings grown 3 years in pots and nearly two growing seasons
outplanted in the field averaged 22 mm (0.9 in) in trunk diameter
(16) by early autumn. The following year trunk diameter increased
4 min (0.15 in).
Dormant nursery-grown seedlings can be stored, barerooted, at
about 0° C (32° F) for several weeks before outplanting
with no appreciable loss in survival rate (15).
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Soils and Topography
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Honeylocust is found most commonly on soils in the orders
Alfisols, Inceptisols, and Mollisols that originate from
limestone or the rich alluvial floodplains of major rivers and
streams. Growth is poor on gravelly or heavy clay soils and
honeylocust often fails on shallow soils. Although ample soil
moisture is necessary for best growth, the species is very
resistant to drought. Because of this, it is a valuable species
for shelterbelt planting in the Great Plains.
On 20 drought-resistant species of seedlings tested, honeylocust
ranked third in alkali tolerance (7). The species is also
tolerant of acid soils (26), but best development is usually on
soils having a pH between 6.0 and 8.0. From tests incorporating
artificially salinized soils, young honeylocusts were found to be
tolerant of soil salinity (13). Seed germination was little
influenced by as much as 0.20 percent of sodium chloride in the
dry weight of soil (2). Salt tolerance has particular economic
importance in the North where runoff from highway de-icing salts
can damage plantings, and also where plantings are desired on
saline soils in and states. Whether honeylocust can tolerate the
cumulative effects of salinity over a period of years is still
unknown.
Typically, honeylocust is a bottom land species, most commonly
found only on moist fertile soils near streams or lakes. Although
it is not common anywhere in the Mississippi River Delta, it
frequently grows on low clay ridges and flats in first bottoms
and on the secondary flood plains along the Missouri River
tributaries in Nebraska.
Over its range honeylocust grows naturally below a maximum
elevation of 610 to 760 m (2,000 to 2,500 ft), although the
general upper elevational. limit for the species is reported as
1520 m (5,000 ft). A 20year-old plantation growing at 2100 m
(6,900 ft) in Colorado had "good" survival, but
trees averaged only 2.4 m (8 ft) in height (7).
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Special Uses
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Honeylocust fruits are readily eaten by cattle and hogs. The beans
of some cultivars contain as much as 12 to 13 percent protein,
and the pods contain up to 42 percent carbohydrates (12,20).
Livestock also eat the young vegetative growth and both the fruit
and plants are eaten by snowshoe hares and cottontails. Fruits
are also eaten by gray squirrels, fox squirrels, white-tailed
deer, bobwhite, starlings, crows, and opossum (7,8). Honeylocust
is a source of honey during the short flowering period in spring.
Both the common honeylocust and its thornless varieties are
planted for erosion control and for wind breaks; the thornless
varieties are widely planted as shade and ornamental trees. In
many urban areas thornless honeylocust has been planted as a
replacement for the American elm (26).
The wood of honeylocust possesses many desirable qualities but is
little used because of its scarcity (23).
The sapwood is generally wide and yellowish in contrast to the
reddish-brown heartwood, providing an attractive grain. The wood
is dense, very heavy, very hard, strong in bending, stiff,
resistant to shock, and is durable when in contact with soil. It
is used locally for fence posts, and also as lumber for pallets,
crating, and general construction.
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Vegetative Reproduction
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Honeylocust coppices freely.
Propagation, particularly of high quality clonal stock, can be
achieved by grafting, budding, and cuttings from hardwood,
softwood, and roots (7). Root cuttings appear to be the best
method of reproducing desirable strains in large quantities at
reasonable cost. At times other species or varieties are grafted
onto the rootstock of honeylocust (24).
Honeylocust thorn production usually diminishes gradually and
finally ceases in the upper and outer crown growth as the tree
ages. Thorns may still be produced on the lower trunk and on
lower-trunk and limb sprouts. Typical trees, 10 years old or
more, show a definite thornless region in the upper and outer
shoot growth. When hardwood cuttings for propagation are taken
from this thornless area, the scions generally remain thornless
(6). Tree breeders can control the sex of scions from honeylocust
by selecting unisexual budwood when taking cuttings. Certain
branches bear only one type of flower, and trees from cuttings
from those branches will bear only that type (14).
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Distribution
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Honeylocust is found scattered in the East-Central United States
from central Pennsylvania westward to southeastern South Dakota,
south to central and southeastern Texas, east to southern
Alabama, then northeasterly through Alabama to western Maryland.
Outlying populations of the species may be found in northwestern
Florida, west Texas, and west-central Oklahoma. It is naturalized
east to the Appalachian Mountains from South Carolina north to
Pennsylvania, New York, and New England (11). Honeylocust attains
its maximum development in the valleys of small streams in
southern Indiana and Illinois.
-The native range of honey locust.
Honeylocust, especially the thornless form, is widely cultivated
as an ornamental and shade tree in all countries having a
temperate climate.
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Brief Summary
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Leguminosae -- Legume family
Robert M. Blair
Honeylocust (Gleditsia triacanthos), also called
sweet-locust or thorny-locust, is a moderately fast growing tree
commonly found on moist bottom lands or limestone soils. Because
it has proven very hardy and tolerant of drought and salinity, it
is widely planted for windbreaks and soil erosion control. The
thornless variety has been planted to replace the elm in many
urban areas. The wood is dense, hard, and durable but used only
locally. Honeylocust pods are sweet and eaten by livestock and
wildlife. The tree is relatively short lived, reaching the age of
125 years.
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